From 42a79e41541b1256cf5c9005217e5703e56f392b Mon Sep 17 00:00:00 2001
From: Xi Xu <i@xi-xu.me>
Date: Mon, 28 Apr 2025 09:30:48 +0800
Subject: [PATCH] Create 4

---
 4/calculator_fifo.c      | 36 ++++++++++++++++++++++
 4/collector_calculator.c | 66 ++++++++++++++++++++++++++++++++++++++++
 4/collector_fifo.c       | 45 +++++++++++++++++++++++++++
 4/even_numbers.c         | 33 ++++++++++++++++++++
 4 files changed, 180 insertions(+)
 create mode 100644 4/calculator_fifo.c
 create mode 100644 4/collector_calculator.c
 create mode 100644 4/collector_fifo.c
 create mode 100644 4/even_numbers.c

diff --git a/4/calculator_fifo.c b/4/calculator_fifo.c
new file mode 100644
index 0000000..42e1c8b
--- /dev/null
+++ b/4/calculator_fifo.c
@@ -0,0 +1,36 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+#define FIFO_PATH "/tmp/collector_fifo"
+
+int main() {
+	int fd;
+	int num;
+	int sum = 0;
+
+	printf("Calculator started. Waiting for collector...\n");
+
+	// Open FIFO for reading
+	fd = open(FIFO_PATH, O_RDONLY);
+	if (fd == -1) {
+		perror("Failed to open FIFO");
+		exit(EXIT_FAILURE);
+	}
+
+	printf("Connected! Ready to receive integers.\n");
+
+	// Read integers from the FIFO and calculate the sum
+	while (read(fd, &num, sizeof(int)) > 0) {
+		sum += num;
+		printf("Received: %d, Current Sum: %d\n", num, sum);
+	}
+
+	close(fd);
+	printf("Calculator exiting.\n");
+
+	return 0;
+}
\ No newline at end of file
diff --git a/4/collector_calculator.c b/4/collector_calculator.c
new file mode 100644
index 0000000..8960441
--- /dev/null
+++ b/4/collector_calculator.c
@@ -0,0 +1,66 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+#include <sys/types.h>
+#include <sys/wait.h>
+#include <signal.h>
+
+int main() {
+	int pipe_fd[2];
+	pid_t pid;
+	int num, sum = 0;
+
+	// Create pipe
+	if (pipe(pipe_fd) == -1) {
+		perror("Pipe creation failed");
+		exit(EXIT_FAILURE);
+	}
+
+	// Create child process
+	pid = fork();
+
+	if (pid < 0) {
+		// Fork failed
+		perror("Fork failed");
+		exit(EXIT_FAILURE);
+	}
+	else if (pid == 0) {
+		// Child process - calculator
+		close(pipe_fd[1]); // Close write end of pipe
+
+		printf("[Calculator] Started. Waiting for integers...\n");
+
+		while (read(pipe_fd[0], &num, sizeof(int)) > 0) {
+			sum += num;
+			printf("[Calculator] Received: %d, Current Sum: %d\n", num, sum);
+		}
+
+		close(pipe_fd[0]);
+		printf("[Calculator] Exiting.\n");
+		exit(EXIT_SUCCESS);
+	}
+	else {
+		// Parent process - collector
+		close(pipe_fd[0]); // Close read end of pipe
+
+		printf("[Collector] Started. Enter integers (Ctrl+D to exit):\n");
+
+		while (scanf("%d", &num) == 1) {
+			if (write(pipe_fd[1], &num, sizeof(int)) == -1) {
+				perror("Write error");
+				break;
+			}
+			printf("[Collector] Sent: %d\n", num);
+		}
+
+		close(pipe_fd[1]); // Close write end to signal EOF to child
+		printf("[Collector] Waiting for calculator to finish...\n");
+
+		// Wait for child to finish
+		wait(NULL);
+
+		printf("[Collector] Exiting.\n");
+	}
+
+	return 0;
+}
\ No newline at end of file
diff --git a/4/collector_fifo.c b/4/collector_fifo.c
new file mode 100644
index 0000000..d0f1d68
--- /dev/null
+++ b/4/collector_fifo.c
@@ -0,0 +1,45 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <unistd.h>
+#include <string.h>
+#include <errno.h>
+
+#define FIFO_PATH "/tmp/collector_fifo"
+
+int main() {
+	int fd;
+	int num;
+
+	// Create the FIFO if it doesn't exist
+	if (mkfifo(FIFO_PATH, 0666) == -1 && errno != EEXIST) {
+		perror("mkfifo error");
+		exit(EXIT_FAILURE);
+	}
+
+	printf("Collector started. Connecting to calculator...\n");
+
+	// Open FIFO for writing
+	fd = open(FIFO_PATH, O_WRONLY);
+	if (fd == -1) {
+		perror("Failed to open FIFO");
+		exit(EXIT_FAILURE);
+	}
+
+	printf("Connected! Enter integers (Ctrl+D to exit):\n");
+
+	while (scanf("%d", &num) == 1) {
+		if (write(fd, &num, sizeof(int)) == -1) {
+			perror("Write error");
+			break;
+		}
+		printf("Sent: %d\n", num);
+	}
+
+	close(fd);
+	printf("Collector exiting.\n");
+
+	return 0;
+}
\ No newline at end of file
diff --git a/4/even_numbers.c b/4/even_numbers.c
new file mode 100644
index 0000000..af534e5
--- /dev/null
+++ b/4/even_numbers.c
@@ -0,0 +1,33 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <signal.h>
+#include <unistd.h>
+
+volatile int number = 0;	// Current even number
+volatile int direction = 1; // 1 for ascending, -1 for descending
+
+void handle_sigint(int sig) {
+	// Change direction when CTRL+C is pressed
+	direction = -direction;
+	printf("\nChanging direction to %s\n",
+		(direction > 0) ? "ascending" : "descending");
+	// Re-register the signal handler
+	signal(SIGINT, handle_sigint);
+}
+
+int main() {
+	// Register SIGINT handler
+	signal(SIGINT, handle_sigint);
+
+	printf("Starting program: outputting even numbers\n");
+	printf("Press Ctrl+C to change direction\n");
+
+	while (1) {
+		printf("%d\n", number);
+		number += 2 * direction; // Add or subtract 2 based on direction
+		fflush(stdout);			 // Force output to be displayed immediately
+		sleep(1);				 // Wait for 1 second
+	}
+
+	return 0;
+}
\ No newline at end of file